Theresa May, the home secretary, speaks at the Conservative party conference in Manchester. Photograph: Ray Tang / Rex Features

"I'm not making this up," said the home secretary, as she regaled the Tory faithful with yet another Human Rights Act folly: an "illegal immigrant" could not be deported because he had a cat.

I'll be charitable and accept this wasn't a wilful misrepresentation. But if so, someone in her department evidently failed to brief her on one of its own cases (still "not fit for purpose" eh?)

I'll start with a minor point: the man, a Bolivian, was not an "illegal immigrant". He came to this country quite legally as a student but stayed beyond the expiration of his visa – perhaps May thought that distinction would be lost on a conference audience.

More significantly, his right to remain in this country had nothing to do with his cat. For four years before his case came before the immigration courts the man lived with a British woman. They did all those coupley things: bought crockery, went out clubbing, got a pet cat. When it came to wanting to regularise the man's right to stay in this country – and anticipating immigration officials' inevitable scepticism – the shared cat was one of a number of factors used by the couple as evidence their relationship was genuine.

The couple relied on a Home Office policy that applied at the time (issued in 1996 under the last Conservative government) under which someone who had been in a relationship with a British citizen (or someone of another nationality who was "settled" here) for at least two years would be given the right to stay. The Home Office rejected the application and the couple appealed.

By the time the appeal was heard the policy had been revoked but still applied to existing applications. The immigration judge allowed the appeal for that reason. But he also considered evidence of the couple's relationship, including the cat. The Home Office then appealed, arguing, in part, that the judge had attached too much weight to the cat. At the appeal hearing its barrister conceded the Home Office had failed to understand its own policy (that fitness issue again!) The man was allowed to stay. The ruling had nothing to do with the cat, although the senior immigration judge who heard the case ended her ruling with a rather feeble – and in retrospect unfortunate – joke: the cat "need no longer fear having to adapt to Bolivian mice".

The home secretary is gunning for the Human Rights Act. Her particular gripe is that several people she would like to deport have successfully used article 8 of the European convention on human rights to resist removal.

Article 8 guarantees respect for a person's private and family life. It's not an absolute right: the state can justify interferences if they serve a legitimate purpose and are proportionate. Immigration control is a legitimate purpose, so the issue for the immigration courts on human rights appeals is whether the state's interest in maintaining immigration controls (or in many, but not all, cases, removing people who have been convicted of serious criminal offences) outweighs the proposed deportee's, and his/her family members', right to remain together. Surely, it's right that this balancing exercise is performed? Why is it controversial that decisions made by politicians, subject to outside pressures, are reviewed by the courts?

There is a legitimate discussion to be had about how to balance these competing interests. But let's have this on a properly informed basis. "Catgate" is just one example where the anti-HRA media and populist politicians have misrepresented the facts.

A final bit of legal advice for the home secretary: in a 1970s case against Iceland brought by a man refused permission to keep a pet dog, the European Commission of Human Rights (a precursor of the current court) held that keeping a pet did not come within the scope of article 8. If anyone resists deportation on the grounds that he/she has a cat here, May can use that case.

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